1. Technical Field
The present invention relates generally to wireless communication devices and in particular to wireless communication devices utilized in computer systems. Still more particularly, the present invention is directed to optimizing performance by avoidance of interference.
2. Description of the Related Art
The need for personal wireless communications is expanding rapidly with the advances in digital communications and personal communications systems. The progress in wireless radio technology and the growth rate of the wireless telephone systems over the last several years is indicative of tremendous market demand for location independent communication via wireless access. Many of the current wireless networks architectures are primarily designed and optimized for voice communications and wide area coverage. With the proliferation of personal and portable computers, and local area networks, it is envisioned that data services and applications such as file server access, client-server execution, and electronic mail will require wireless access to the LAN environment supporting distributed computing. The use of wireless communication systems to transmit data traffic utilizing mobile devices which communicate with a hardwired network, such as a LAN has become widespread. In the future mobile workers could be connected everywhere on campus with increased productivity. Retail stores and warehouses, for example, may use wireless communications systems with mobile data terminals to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects. Since reliability of data traffic will become essential, the wireless access protocol must efficiently accommodate the very dynamic nature of interference.
A typical wireless communications system includes a number of fixed access points (also known as base stations) interconnected by a cable medium often referred to as a system backbone. Associated with each access point is a geographic cell. The cell is a geographic area in which an access point has sufficient signal strength to transmit data and receive data from a mobile device such as a data terminal or telephone with an acceptable error rate. Typically, access points will be positioned along the backbones such that the combined cell area coverage from each access point provides full coverage of a building or site. In the case of WLAN (Wireless LAN), frequently there are significant overlaps in cells to increase data capacity. So a user typically has access to several different access points in any given location. The reason for this is that the capacity of the network is a function of the number of access points. For 802.11 b network, an access point provides 11 Mbps, which is shared by number of users.
Mobile computers with WLAN are designed to be carried throughout the system from cell to cell. Each mobile device is capable of communicating with the system backbone via wireless communication between the mobile device and an access point to which the mobile device is registered. As the mobile device roams from one cell to another, the mobile device will typically deregister with the access point of the previous cell and register with the access point associated with the new cell.
Recently, a standard for wireless local area networks (WLANs) known as the IEEE 802.11 standard has been adopted and has gained wide spread acceptance in the industry among computer users. The IEEE 802.11 standard for WLANs is a standard for systems that operate in the 2,400-2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The IEEE 802.11 RF transmissions use multiple signaling schemes (modulations) at different data rates to deliver a single data packet between wireless systems. The latest IEEE 802.11 wireless LAN uses a band of frequencies near 2.4 Ghz for direct sequence spread spectrum transmissions.
The RF spectrum is a limited bandwidth spectrum that is allocated among a number of different services types/applications, including military, aviation, broadcast, and commercial communications. Because of the very limited bandwidth available within the radio frequency (RF) spectrum, transmission in this medium is subject to strict government regulations. The regulations typically cover the type and parameters of the transmitters being utilized in a wireless network. These regulations cover modulation scheme, frequency of operation, and transmit power of the transmitters in order to avoid interference among the various authorized services utilizing the RF spectrum.
Another recently adopted short-range standard has evolved known as the Bluetooth standard. The Bluetooth standard is a low-cost short range wireless connection which uses much of the same range of frequencies for its frequency-hopping spread spectrum transmissions as the IEEE 802.11 standard. Bluetooth is considered a personal area network (PAN) since it is limited to short range distance 30 ft and was designed as a cable replacement technology. Bluetooth replaces the cables that previously connected Personal Computers or other client devices to peripherals such as printers, headphones, and PDAs.
The ISM band (2.4 Ghz band) allows for a shared transmission medium between the various technologies 802.11 b, Bluetooth, and other devices such as cordless phones and microwave ovens. A client device has the ability to associate with various access points, but will select based on priority order or first response. Current methods to select which access point to associate with do not consider the adverse effect of noise from other devices in 2.4 Ghz band. Therefore, a client may select an access point such that the transmission path to the client is subject to interference from other devices instead of a clear path, with no interference, to another access point. Accordingly, there is a strong need in the art for a system and method that allows a client, on the wireless LAN, to associate with access points to minimize interference.